The present invention relates to a rear block, a rear floor, and reinforcement for a motor vehicle.
More precisely, the invention lies in the field of protecting the rear ends of vehicles against high speed impacts.
In the present application, the chassis 100 of a vehicle is defined as a rigid structure, as can be seen in FIG. 0 which is a diagram representing the body of a prior art vehicle, that includes a non-deformable survival cell so as to protect the passengers in the event of an impact. The chassis presents two front longitudinal rails 102 and two rear longitudinal rails 104 providing bearing points for a front impact beam 106 and a rear impact beam 108. The term “underbody” 110 designates the side portions of the chassis in the survival cell, and the term “structural nodes” 112 designates the two intersections of the underbody 110 with the rear longitudinal rails 104.
In the event of a rear impact, a fraction of the energy of the impact is absorbed by deforming the rear block, in particular the beam 108 and the longitudinal rails 104. The remainder of the energy is transmitted in the form of kinetic energy to the chassis 100, which does not deform and thus preserves the passengers. The nodes 112 are designed to take up the forces received by the longitudinal rails from behind and to transmit them to the chassis. The nodes 112 may also be situated at the intersections between a cross-member 114 and the longitudinal rails, and may constitute the interface with the rear axle for transmitting vertical or transverse forces stemming from contact with the road. Consequently, the nodes 112 constitute very rigid connections, particularly since the bonding between these parts is generally performed by welding, thereby contributing to providing stiffness. By definition, the nodes do not have an energy-absorbing function, and they are considered as being non-deformable for impacts up to 80 kilometers per hour (km/h).
Such a structure is not fully satisfactory in the event of a high-speed impact against only part of the rear end of the vehicle, for two reasons. Firstly, when the point of impact is situated on one side of the rear end of the vehicle, only one of the two longitudinal rails is under stress to resist the impact, even though the impact is particularly violent and the rail needs to provide maximum resistance. Secondly, when the point of impact is situated between the two longitudinal rails, the impact beam 108 is highly stressed in bending and might break.
One means is already known in the prior art for responding to those drawbacks, namely providing a third longitudinal rail between the other two. This third longitudinal rail extends between the impact beam 108 and the opposite cross-member 114. It thus enables energy due to an impact to be absorbed better by forming a third bearing point for the beam.
However, when the impact covers only a portion of the rear end of the vehicle, the force is transmitted to the chassis, and more precisely to the underbody 110, via the cross-member, such that the total force that can be accepted by the rear block is limited by the bending strength of the cross-member 114. In addition, the third longitudinal rail runs the risk of penetrating into the survival cell or into the fuel tank.